This invention relates to highly compactable zirconium sponge which has previously been crushed, wherein prior to crushing, the sponge has been specially treated to give, upon crushing, a modified particle configuration which lends to subsequent compacted articles of improved physical properties.
Conventional, as-reduced, zirconium sponge is occasionally broken up by crushing into small particle sizes and used to make compacted parts according to conventional powder metallurgy practices. Zirconium sponge, however, is not an easily crushed material as it tends to deform plastically rather than fracture. This characteristic results in material which is not readily compacted to dimensional shapes, since some of the sponge particles have in essence been pre-compacted during the crushing.
It is known that metal hydrides, typically of the formula MH.sub.2, wherein M is a metal capable of reacting with hydrogen, are characteristically brittle. This characteristic lends to the manufacture of particulate metals. For example, a piece of metal may be heated and exposed to hydrogen gas for a period of several hours, after which the metal becomes substantially hydrided. Typically, by such processing the metal absorbs about one to about three or more percent by weight of hydrogen, and becomes brittle and more easily comminuted to powdered form. In U.S. Pat. No. 4,300,949, the disclosure of which is incorporated by reference, a method is disclosed whereby metal is heated in the presence of hydrogen while concurrently being subjected to mechanical impact to obtain a particulate hydride of average particle size of less than about one centimeter. Plasma generators, such as disclosed in U.S. Patent Nos. 3,803,403; 3,843,352; 3,848,068; and 4,655,825, have been used in various contexts in connection with the preparation or treatment of reactive metal hydrides. The process of U.S. Pat. No. 3,803,403 utilizes a plasma arc to generate spherical, non-friable particles which can be fabricated into an article for use as a hydrogen storage device. U.S. Pat. No. 3,843,352 utilizes a gas plasma in a cooled metal crucible to melt sponge metal. U.S. Pat. No. 3,848,068 vaporizes metal powder with a plasma and rapidly quenches the vapor to obtain ultra pure finely divided metal compounds, such as metal hydride. The plasma gas may contain up to 100 percent hydrogen.
As described in U.S. Pat. No. 4,728,507, metal hydrides, for example, zirconium alloy hydrides, are produced by introducing the metal to a melting zone under conditions which form individual droplets of the metal. These droplets are exposed to a hydrogen atmosphere as they are cooled to a temperature which promotes the desired degree of hydrogen absorption, e.g., 0.5-1.0% by weight, which renders the droplets friable for use in powder metallurgy. The U.S. Pat. No. 4,655,825 patent suggests the complete hydriding of metal sponge obtained directly from a conventional zinc alloying and distillation process, and its subsequent comminution for use in powder metallurgy.
These patents are concerned, in varying degrees, with the hydriding of metal or sponge of the Group IV-b and V-b metals, however, those efforts appear to have been of a general nature and not contemplative of the particular problems associated with producing from "as-reduced" zirconium, a powder of exceptionally high compactability for use in powder metallurgy.
A principal object, therefore, of the present invention is to provide a non-complex process for preparing highly compactable, crushed zirconium from "as-reduced" sponge using essentially conventional vacuum furnace equipment, in a highly efficient and economical manner.